High resolution H band imaging polarimetry of IRC +10216

Abstract

We have carried out an H band imaging polarimetry of an evolved AGB star IRC +10216 using CIAO and AO on the Subaru telescope. Our polarimetric images show NE-S bipolar lobes, a NW lobe, a discrete NW arc with ~4.2 arcsec radius and two new features of a fan-like shape at the SE and of an elliptic shape at the NW with small polarizations (P<4%) near the intensity peak. The polarization vectors in the NE-S lobes and the NW lobe have a centrosymmetric pattern centered at the position of the illumination source (the central star). The illumination source is located at (+0.25 arcsec, -0.065 arcsec) from the intensity peak between the SE fan and the NW ellipse. The polarization vectors between these two features are aligned along a line across them. We interpret that the appearance of the SE fan and the NW ellipse reflects a sudden increase of the mass loss rate that likely initiated the formation of an edge-on dust torus. This sudden mass loss increase probably began about a half century ago.